The unifying theme of the Program Project is that the remodeling of the developing heart tube into a four-chambered heart is a series of converging cellular and molecular pathways that regulate the origins, remodeling and ultimate fate of the endocardial cushions. Formation of these cushions is an early defining event for valvuloseptal morphogenesis which is pivotal for remodeling the single heart tube into four separate but precisely aligned chambers. The program project seeks to evaluate the orchestration of multiple cell interactions, modulation of cell migration, and segmental patterning and remodeling events that define the origin and fate of the cushions. Project I investigates the molecular pathways that lead to the initial formation with valvuloseptal cushion formation and the cellular interactions that impart different fates to these cushion-forming segments and, thereby, create a final common pathway for potentially defective heart remodeling. Project II, will investigate the role of myocardialization in valvuloseptal morphogenesis of the developing heart and the functional role of TGFbeta in regulating this process using an in vitro assay to determine whether myocardialization is the driving force for segmental and septal alignment of the atrioventricular junction. Also, the role of epicardial-derived cells in regulating mesenchymal cell formation, proliferation, and differentiation of the endocardial cushions will be studied. Project III will focus on the VEGF/VEGF-receptor, Tie2/Angiopoietin, and the ephrin-B2 signaling pathways and their impact on initial pattern of assembly of the endocardial tube prior to cushion formation. Project IV, will study the dynamic interactions between cells of the heart and extracellular matrix, focusing on proteins in valvuloseptal development. Project V, will focus on characterizing the effects of fibulin-1 on valvuloseptal morphogenesis and explore the underlying mechanisms for the suppressive effects of fibulin-1 on cell motility and determine the effect of altered fibulin-1 expression in vivo. This program project integrates diverse methodologies (morphology, molecular, bioassays and live imaging) and established investigator expertise to create a unique research environment to determine the underlying mechanisms of normal and abnormal development.